1. Field of the Invention
The present invention relates generally to the design and manufacture of disk drive head suspensions. In particular, the present invention is a head suspension having weakening structures for causing the profile of the suspension to be optimized for resonance performance.
2. Description of the Related Art
Head gimbal assemblies (HGAs), also sometimes known as head suspension assemblies (HSAs), are commonly used in rigid magnetic disk drives to support magnetic heads in close proximity to the rotating disk surfaces. Suspension assemblies of this type typically include an air bearing head slider assembly, also sometimes known as a transducer assembly, mounted to a suspension. The suspension includes a load beam having a mounting region on its proximal end and a gimbal or flexure on its distal end. When incorporated into a disk drive the mounting region is mounted to an actuator or positioning arm which supports the suspension assembly over the rotating disk. A baseplate is typically welded to the mounting region to increase the rigidity of the mounting region and to provide a mechanism for securely mounting the suspension assembly to the positioning arm. The load beam is an elongated and often generally triangularly-shaped member which includes a spring region adjacent to the mounting region, and a relatively rigid region which extends from the spring region. The flexure can be manufactured as a separate member and welded to the distal end of the load beam, or formed as an integral member in the distal end of the load beam. The air bearing head slider assembly contains a magnetic head and is typically bonded to the flexure by adhesive. The flexure allows the head slider assembly to move or "gimbal" (about rotational pitch and roll axes) with respect to the distal end of the load beam and thereby follow variations in the surface of the spinning disk. To enable the pivotal flexure movement, the surface of the flexure to which the head slider assembly is bonded is typically spaced from the adjacent surface of the load beam by structures known as load point dimples or formed offsets.
Suspensions are commonly manufactured by chemically etching flat or unformed load beam blanks from thin sheets of stainless steel. Flat and unformed flexure blanks are etched in a similar manner from sheets of stainless steel. During subsequent manufacturing operations side rails, load point dimples and any other structures which extend upwardly or downwardly from the web or generally planar surface of the load beam are formed on the load beam blanks by mechanical bending procedures. Any dimples, offsets or other structures on the flexures requiring deformation of this type are formed in a similar manner. After forming, the flexures are welded to the distal end of the load beams. Baseplates are also welded to the suspensions following the forming operations.
The product of these etching, welding and forming operations are generally flat suspensions (i.e., the mounting region, spring region and rigid region of the load beam are generally coplanar and at the same height. During subsequent manufacturing operations the spring region of the load beam is rolled around a curved mandrel or otherwise bent in such a manner as to plastically bend or permanently deform the spring region. The rolling operation imparts a curved shape to the spring region and causes the flexure to be offset from the mounting region when the suspension is in its unloaded or free state, and impart a "gram load" (described below) to the suspension. The profile can be generated by forming, stamping, rolling, warping (through use of a laser or other techniques for localized heating). The gram load imparted to the suspension also affects the suspension profile. Typically, the load beam will require multiple forming or heating steps to deform the load beam to the "optimal" profile with the desired gram load.
As noted above, the suspension supports the slider assembly over the magnetic disk. In reaction to the air pressure at the surface of the spinning disk, the slider assembly develops an aerodynamic force which causes the slider assembly to lift away from and "fly" over the disk surface. To counteract this hydrodynamic lifting force, the head suspension assembly is mounted to the disk drive with the suspension in a loaded state so the bent spring region of the suspension forces the head slider assembly toward the magnetic disk. The height at which the slider assembly flies over the disk surface is known as the "fly height." The force exerted by the suspension on the slider assembly when the slider assembly is at fly height is known as the "gram load."
An important performance-related criteria of a suspension is specified in terms of its resonance characteristics. In order for the head slider assembly to be accurately positioned with respect to a desired track on the magnetic disk, the suspension must be capable of precisely translating or transferring the motion of the positioning arm to the slider assembly. An inherent property of moving mechanical systems, however, is their tendency to bend and twist in a number of different modes when driven back and forth at certain rates known as resonant frequencies. Any such bending or twisting of a suspension can cause the position of the head slider assembly to deviate from its intended position with respect to the desired track. Since the head suspension assemblies must be driven at high rates of speed in high performance disk drives, it is desirable for the resonant frequencies of a suspension to be as high as possible. The detrimental effects of the bending and twisting at the resonance frequencies can also be reduced by minimizing the extent of the bending and twisting motion of the suspension (also known as the gain) at the resonant frequencies.
Common bending and twisting modes of suspensions are generally known and discussed, for example, in the Yumura et al. U.S. Pat. No. 5,339,208 and the Hatch et al. U.S. Pat. No. 5,471,734. Modes which result in lateral or transverse motion (also known as off-track motion) of the head slider are particularly detrimental since this motion causes the head slider to move from the desired track on the disk toward an adjacent track. The three primary modes which produce this transverse motion are known as the sway, first torsion and second torsion modes. The sway mode is a lateral bending mode (i.e., the suspension bends in the transverse direction along its entire length). The first and second torsion modes are twisting modes during which the suspension twists about a central longitudinal axis which extends from the mounting region to the flexure through the suspension's center of rotation. The first and second torsion modes produce transverse motion of the head slider if the center of rotation of the suspension is not aligned with the head slider.
Various techniques for compensating for the detrimental effect of resonance modes are known. The Yumura et al. U.S. Pat. No. 5,339,208, for example, discloses load beam structures having a shear center at the gimbal contact point between the flexure and load beam. The Hatch et al. U.S. Pat. No. 5,471,734 notes that the position, shape and size of the roll or bend in the spring region of the suspension, characteristics sometimes referred to as the radius geometry or radius profile of the suspension, can affect resonance characteristics. The Hatch et al. patent also discloses a fabrication method which uses computational finite element analysis to optimize the suspension radius region and dynamically decouple the head slider from the torsional motion of the rest of the suspension and/or to maximize the resonant frequency of the sway mode.
Oftentimes, the geometry of the side rails incorporated into a suspension do not provide optimal resonance characteristics (gain or frequency). To provide optimal resonance characteristics, the discrete cross sectional center of gravity and shear center can be specifically adapted to the application. However, volume constraints, wire routing and other complications usually dictate compromises which result in the use of non-optimal rail configurations (e.g., the commonly used "L"-shaped rails). As noted above, in these instances the profile of the suspension (e.g., the position, shape and size of the roll in the spring region) is used to move the center of gravity and shear center locations to enhance the resonance characteristics.
It is evident that there is a continuing need for suspensions having improved resonance characteristics. Suspensions optimized for several resonance characteristics would be particularly advantageous. To be commercially viable, the suspensions must be efficient to manufacture.